Wikipedia:Reference desk/Archives/Science/2012 December 4

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December 4

How long do water molecules last (live?)

If a snowflake falls on a glacier, (3.5 x 10^19 molecules to a snowflake I read)...and we could follow one molecule when the snow melts, the water runs into a river, then to the ocean, and then at some point evaporates becoming clouds, and pushes onshore to fall as snow again...does that one water molecule exist throughout, changing states from solid to liquid to gas, around and around? Forever? Does something break up an H20 molecule at some point? Does a water molecule have a birth, life, death, or will some of them go around and around for years, ages, eons? How does it work? Thanks if you can help me understand and picture it. — Preceding unsigned comment added by 94.208.75.76 (talk) 03:10, 4 December 2012 (UTC)

Water molecules in liquid and solid change their specific atomic associations over time (exactly which two H are attached to exactly which O). The origin of "neutral water pH is 7" is that some aren't even associated as a 2:1 form at all. See self-ionization of water. DMacks (talk) 03:17, 4 December 2012 (UTC)

I am wondering though, at any point do H2O molecules cease to be H2O molecules? For instance are there any naturally occurring events or processes causing H2O molecules to cease to exist? Do any H2O molecules drift off as hydrogen atoms and oxygen atoms? Or do any hydrogen atoms and oxygen atoms combine with other atoms or molecules to form new substances? Conversely, are there any naturally occurring processes on Earth which create H2O? Bus stop (talk) 04:40, 4 December 2012 (UTC)

There are certainly biological processes which do both. Also, an acid plus a base produces a salt plus water, and that reaction happens in nature both inside and outside of organisms. StuRat (talk) 04:46, 4 December 2012 (UTC)

Also, I'd expect water ice to be more stable than either liquid water or water vapor. On Earth, water ice tends to only last for a few hundred thousand years, in Antarctica, say. However, liquid ice deep inside Pluto or beyond might have formed when the solar system formed, some 4.3 billion years ago, and never melted since (unless tidal forces from Charon (moon) heat it enough to melt the ice). In that case, those molecules should mostly be the same as they were when formed. StuRat (talk) 04:57, 4 December 2012 (UTC)

• In quantum mechanics, particles do not have individual identities that persist over time, and molecules, which are arrays of particles, don't either. When two water molecules come close enough together for their wave functions to overlap, it is impossible even in principle to say which is which afterward. So really the question is meaningless, and some of the responses above are too. Looie496 (talk) 05:50, 4 December 2012 (UTC)

Atoms with individual identities

• • I don't know that you can say that it is impossible to identify individual atoms with individual identities. I mean, this picture does a pretty good job of that. Those bright spots are individual carbon atoms, and the entire structure is a macromolecule known as a carbon nanotube. You can not only resolve the structure as a whole, but individual carbon atoms within it. --Jayron32 07:01, 4 December 2012 (UTC)

If we consider an oxidanyl group to be the core of a water molecule, how long is the average lifespan above sea level an oxidanyl group with nothing else attached, besides more hydrogen? Plasmic Physics (talk) 06:05, 4 December 2012 (UTC)

Certainly we can calculate the rate of the reverse reaction of H2O --> 1/2 O2 + H2. It's vanishingly small, but finite at 300K ==> long but finite lifetime. John Riemann Soong (talk) 06:12, 4 December 2012 (UTC)

Please do. I'd be interested to know if they last thousands, millions, billions, or trillions of years. StuRat (talk) 06:16, 4 December 2012 (UTC)

Such a calculation is not trivial, as this is not a single step, or elementary ("single hump") reaction. It involves in theory an infinite number of component reactions. However, if only high "engineering" accuracy results are required, you can ignore intermediate forms occuring at less than parts per million concentrations - then the species involved will be limitted to:-

H

H₂ (end)

O

O₂ (end)

O₃

OH

HO₂

H₂0 (start)

H₂O₂

A total of 136 competing elementary reactions occur between these 9 species. If anyone wants to know what they are, ask, and I'll post.

There are two approaches to the calculation: 1) use the mathematics of dissociation. This requires knowing the enthlapy of formation of each species (no problem, you can look it up in standard tables), writing the dissocation equation, and solving for the roots of the equation. Therein lies a problem - the calculation converges very very slowly on to the roots - days and days of computer time is required (assuming a typical up to date PC), and it is so darm easy to make a mistake in writing the equation. When you get the answer, you'll find the overall reaction rate is so slow, like one molecule every few hours or something, the result can't be valid on relativistic grounds. 2) use reaction rate data in the modified arrhenious equation for each of the 136 reactions, and solve 136 non-linear simultaneous reactions for the overall rate. That has two problems - a) good data is not readily available for all the reactions, so some devious pondering is required, b) solving 136 non-linear reactions is going to take some serious computer time.

However, if you only want to know roughly, you can ignore O₃ and cut it down to 40 or so reactions.

Ratbone 120.145.182.171 (talk) 07:00, 4 December 2012 (UTC)

I like it rough, so please proceed. StuRat (talk) 07:04, 4 December 2012 (UTC)

Who, me? Or John RS? I accept bribes if they are large enough. But even then, you won't get an answer (even a rough answer) until long after this question has been archived. Ratbone 120.145.182.171 (talk) 07:14, 4 December 2012 (UTC)

OK, never mind then. StuRat (talk) 20:37, 4 December 2012 (UTC)

Hmmmm, I think you're looking for the "hydrogen exchange rate" or perhaps "proton exchange rate", "hydrogen-deuterium exchange rate" etc. Looks like [1][2][3][4] might be useful but I haven't accessed; the first abstract says OH- exchange predominates (for water in organic solvents). There are sites like [5] for proteins and surely water is a simpler case. I haven't found your number yet but the truth is definitely out there. Wnt (talk) 01:51, 5 December 2012 (UTC)

centripetal acceleration and linear acceleration, assuming "constant effort"

Linear plot of the "w1118" genotype

Logarithmic plot of the "fumin" genotype

Following literature concerning velocity and curvature, I decided to explore the power law among my fruit flies by taking their trajectory data and plotting log v against log R for each fly, where R is 1 over the calculated instantaneous curvature at a point. If v = K * R^b, the slope of this plot should be b and the intercept log K. Different genotypes (at least 4 different ones) appear to have per-fly average slopes ranging from 0.465 to 0.499, often with statistically significant differences between the averages: i.e. 95% confidence intervals are on the order of +/- ~0.008 whereas the difference between w1118 and fumin is ~0.03. To the right are two histograms of two genotypes, each a histogram of a collection of 60-75 flies over 4-5 experiments per genotype. One histogram has frequency colored linearly, and the other has frequency colored logarithmically-- I'm doing this to highlight different aspects of my analysis. Despite the differences, the values of the slope imply that b would be almost half, which would be consistent with centripetal acceleration being constant, since if v^2/R = K^2, where K is some constant, then v = K * R^0.5, consistent with the power law. It's the small deviations from this law that are interesting, since I think this is what separates different genotypes from each other.

The Spearman correlation (or even just the plain old Pearson r) is quite decent, on the order ~0.85. However, there is much overlap between the genotypes' distributions, though the means are statistically significantly different probably because of each genotype's sample size being on the order of n = 60-75. I was thinking that part of the spread in the plot could be due to the fact that centripetal acceleration isn't really constant and as linear acceleration will vary too, if we assume that the total "effort" would be nearly constant or fall within a tight range.

I'm actually surprised that my fit is that good, so I'm thinking, how do I get even tighter distributions that can distinguish between genotypes? The thing is, I can't think of what relation would constrain linear acceleration and centripetal acceleration together. I don't think it's really accurate to model linear acceleration + centripetal acceleration = constant, because I think the centripetal acceleration in an arbitrary non-circular path would include portions of linear acceleration. (And centripetal acceleration is a fictitious force and all that, so one might imagine it as a convenient way to talk about linear acceleration in a different reference frame.) Yet I don't think centripetal acceleration = linear acceleration either, even if we model an arbitrary path as the sum of tiny circular paths with ever changing radii (and directions) of curvature. (Ideally, each circular portion is infinitesimal in size, but we sample only at 15 Hz.)

The idea that effort is constant isn't too ridiculous, because the flies' activities are being driven by super-intense blue light (the wavelength they are most sensitive to) and if they rest, they only rest for a brief moment. You can see that to avoid taking the log of 0, and avoid the effects of noise at the same time, I've filtered all the data points where velocity dipped below 0.1 mm/s (that is, all points below log v = -1).

The basic power law relation I'm using predicts that velocity should be infinite for a straight-line path (infinite curvature), and that curvature should be infinite at zero velocity. Some literature offer a correction of R_eff = R / (1 + alpha*R), where infinite R would imply a finite R_eff of 1/alpha, so K*(1/alpha)^b would be the "max velocity". Curiously, I don't appear to have hit the upper limit of this relation, because the straight-line trend without the correction appears to carry to 90 mm/s (log v = ~2, the upper cutoff point, to avoid using data with random tracking errors, which are usually detectable because velocity is some ungodly amount for flies, like 360 mm/s), and using this correction generally makes the overall linear trend worse. In an arbitrary path model, would centripetal acceleration be basically linear acceleration even for seemingly straight line paths? How do I come up with a better "constant effort" model that would also account for the change in intercept (and in the transition zone, slope) at low velocities ? John Riemann Soong (talk) 05:54, 4 December 2012 (UTC)

${\displaystyle }$

One problem with your model is that in an ideal world the fly has to expend no power on a continual basis in order to generate centripetal acceleration whereas to accelerate in a linear fashion requires power. Do you have a model for the L/D ratio of the fly? Do you think the flies perform at their aerobic maximum, or are strength limited? Greglocock (talk) 22:39, 5 December 2012 (UTC)

I'm measuring walking, not flying. The calculated (supposed) centripetal forces are on the order of ~0.02g. Flight muscles are likely to be stronger than leg muscles (are they actually?) but since a fly has to generate at least 1g of lift during flight, probably on the order of several g for rapid ascent, I think the flies are aerobic-limited? How do I modify the equations for general planar motion if there is friction? Or can I use the equations as is? Are you saying that flies should not be using any energy in centripetal acceleration but my model is not reflecting that? My flies are being confined to a 2D planar arena (they are forced to walk), so I'm trying to wonder what a "real walking" model should include.

If there is friction, tighter turns should require more energy and effort, right? John Riemann Soong (talk) 03:17, 6 December 2012 (UTC)

Also, there is an observed 1/3 power law in idealized handwriting and eye saccades, and some other movements-- this is in the presence of friction. Both a "minimum jerk" model (a criterion for smoothness) and the viscoelastic model (reducing strain on a nonpoint body) are suggested as origins of the trend. John Riemann Soong (talk) 03:20, 6 December 2012 (UTC)

In a frictionless world with no losses centripetal acceleration requireds no continual power input, whereas linear acceleration does. That means it is a lousy model for walking. Frankly I doubt that walking in circles uses more power than walking in straight lines. Perhaps it would preferentially tire one set of muscles. Sorry, i can't think of a way to help you further. Greglocock (talk) 22:55, 6 December 2012 (UTC)

Mauser 98

Does the Mauser 98 give any positive indication when the ammo in the magazine runs out? In other words, when the shooter fires off the last cartridge, how does he (she) know that it's time to reload (other than by counting shots)? 24.23.196.85 (talk) 06:51, 4 December 2012 (UTC)

While there may be variations - after all the Mauser 98 action was manufactured for a long time and for a great many customers - my M59F1 (built from an ex-german M98k receiver) has a knob on the magazine follower that will hold the bolt back when the magazine is empty. Only way to close the bolt is to fill the magazine or push the follower down with a finger - it is natural to assume that such a device is common to most or all M98 actions. WegianWarrior (talk) 09:16, 4 December 2012 (UTC)

This article on the The 1896 Swedish Mauser says "After the last round fired and ejected, the follower locks the bolt open for rapid reloading", although this was an earlier design than the M98. However, the Persian vz98/29 Mauser (made in Czechoslovakia for Persia (Iran)) " It’s useful that the magazine platform does not lock the bolt open after the last round has been fired and ejected. As an idiot’s guide it’s probably useful to show some thick squaddy that the gun is empty, but not required for the sort of shooting we do." So it looks a bit variable. Alansplodge (talk) 14:37, 4 December 2012 (UTC)

Thanks! I was asking specifically about the Karabiner 98k version used by the German Wehrmacht during World War 2. 24.23.196.85 (talk) 22:47, 4 December 2012 (UTC)

This page has some downloadable instruction manuals for the 98k. This simplified manual for a late-WWII 98k doesn't mention it. Alansplodge (talk) 17:01, 5 December 2012 (UTC)

Thanks, Alansplodge! I've checked the manual, and it says nothing about the bolt locking back when the magazine is empty. So, I can safely infer that the only way to know for sure is to count your shots -- and if you happened to take the rifle from an enemy who fired it and hadn't reloaded (as my character has done), you're in danger of ending up with an empty mag without knowing it. 24.23.196.85 (talk) 01:41, 6 December 2012 (UTC)

what's the differences between forged steel and wrought steel?

what's the differences between forged steel and wrought steel?thanks a lot. — Preceding unsigned comment added by 121.15.133.68 (talk) 06:54, 4 December 2012 (UTC)

Do you mean how they are made, their properties, appearance, or what ? StuRat (talk) 07:00, 4 December 2012 (UTC)

I've never heard of "wrought steel". There is Wrought iron, which is, I suppose, an ultra low carbon steel. Its properties can be compared to Steel itself, by looking at both of those articles. --Jayron32 07:41, 4 December 2012 (UTC)

This page describes wrought steel as carbon steel that is shaped by rolling rather than casting. Looie496 (talk) 19:12, 4 December 2012 (UTC)

The term "wrought" is a little bit confusing, because it refers to both a process of working metal; and also to a chemical recipe for certain types of metal (usually iron) that are soft enough to be useful for that style of metalwork. In this case, wrought steel is referring to steel that has been worked. See also, wikt:wrought. In fact, ASME (an organization that is generally well-regarded for its expertise in the fields of materials science and engineering) has standards related to wrought iron, wrought copper, wrought steel, ... the list goes on and on. I have never personally worked with anything called "wrought copper," but nonetheless, there's at least one ANSI standard for it, (ANSI/ASME B.16), and in fact there are entire trade organizations centered around it. Nimur (talk) 15:27, 5 December 2012 (UTC)

TEXTABLE LANDLINE TELEPHONES! - Where can I buy one?

If you know the correct article title, you may edit the original dead-end WL to it.

I've been searching high-and-low for landline phones that can send and receive SMS, but even Best Buy has none. Why are they so hard to come by???

If they're not available in the good ol' US of A, then what are some GREAT textable landline phone models that I can order from overseas? (Or if there are some textable landline models sold from some online specialty stores that are physically located in a US warehouse, that's even better due to reduced shipping costs!)

I vow NEVER to get a landline until I find one that sends and receives texting. Why are they so hard to find in America in the first place? Thanks kindly. --70.179.167.78 (talk) 08:29, 4 December 2012 (UTC)

Once you have the phone, then what? Have you evidence that American phone companies have the ability to send text messages to a land line phone? I've never heard anything about that being possible. Which isn't to say it's not but it's not that popular. Dismas|^(talk) 09:08, 4 December 2012 (UTC)

The American landline phone standard, POTS, was designed decades ago and while they have expanded the service options over time, the system generally does not support text messaging (i.e. SMS). Some of the landline alternatives, such as home VoIP through an internet service or digital phone from a cable company, may offer SMS options but they are still rare in my experience. You should verify that the phone service you want to use supports text messaging at all, before worrying about where you can find compatible phones. Dragons flight (talk) 10:54, 4 December 2012 (UTC)

If you can use a landline, you must be in a building. And if you are in a building, you can use a PC to access the internet. And if you can do that, great, because many phone companies offer a website that lets you send an SM to a mobile phone on their network. Nobody can send an SMS to you though. Why not use email? Or just phone them? Ratbone 124.182.41.70 (talk) 11:32, 4 December 2012 (UTC)

The people above are correct - the land line phone system doesn't support SMS. SMS is only possible on mobile phone networks. You can also email texts to cell phones - each carrier has a different format for the address associated with a phone number. You can also send a text message to an email address via SMS on the phone. There are devices that connect to the mobile phone network and let you plug a landline phone into them, but I can't recall what they are called. Perhaps one of those has SMS built in, but you would have to access it from the base, not the landline phone plugged into it. 209.131.76.183 (talk) 13:15, 4 December 2012 (UTC)

actually, IIRC, texting goes via the same path as the caller id; which is at least optionally available on landlines. so in principle, it should be possible? Gzuckier (talk) 18:40, 4 December 2012 (UTC)

No, it's very different. In North America the CID burst is an analog frequency-shift-key encoded sequence (a Bell 202 variant) transmitted in-band (and if the phone is off-hook, preceded by a DTMF-like alert tone); arrangements in different phone systems are similar. SMS is an out-of-band digital message type sent as a Mobile Application Part message on a GSM digital connection. There is no agreed upon standard (at least that I've ever heard of anyone actually implementing) for wrapping SMS in an in-band (FSK, QAM, whatever) burst. ISDN, which does support wrapping additional protocols in messages in a D channel, can support SMS, and some ISDN handsets do (but I don't know how standard and interoperable this really is). -- Finlay McWalterჷTalk 18:55, 4 December 2012 (UTC)

Fax it: send and receive text. --VanBurenen (talk) 19:21, 4 December 2012 (UTC)

May I ask, what about a land-line do you actually want ? The more comfortable headset ? Not having to charge it ? Or something else ? Because, if you have a cell phone already, a land line does seem like an unnecessary expense these days (although I have one, since it's bundled with my Internet). StuRat (talk) 20:35, 4 December 2012 (UTC)

Sound quality is usually better on land lines. --Trovatore (talk) 00:29, 5 December 2012 (UTC)

I asked pretty much the same thing Wikipedia:Reference desk/Archives/Science/2011 December 30#What'll it take to upgrade landline networks to allow texting to and from landline phones? but never received a response from the OP (which doesn't seem uncommon for them). Me and Astronasut made a similar point to Dismas and most other respondents basically touched on similar ideas as to the above discussion but this doesn't seem to have been take on board either. Nil Einne (talk) 23:00, 4 December 2012 (UTC)

It does seem like the companies offering landlines have concluded that their extinction is inevitable, and thus decided to invest the bare minimum to keep them operational until that time. So, any R&D, such as into supporting texting, is off the radar. StuRat (talk) 00:22, 5 December 2012 (UTC)

wandering offtopic here, but the reason i keep the old landline is that it was built to survive nuclear war, so the odd hurricane won't phase it. whereas isdn lines and cell towers are more fragile. of course, eventually, there will be nobody for me to talk to call from my cold and dark house in the disaster area. Gzuckier (talk) 06:05, 5 December 2012 (UTC)

I'll talk to you! I hope landlines don't go away. I like being able to make calls indoors - I see people standing out in their yard so they can get reception. Also, if I dial 911 they know where I am. Also, it is so easy to use: just pick it up to talk, put it back down to hang up - no extra buttons to press. And my cable goes out so often - if I relied in them for the phone it would be out of order a considerable part of the time. And the landline doesn't drop out! And, perhaps most of all, is the sound quality. Cell phones have terrible sound quality. I think it is bad manners to call someone with a cell phone unless there is no alternative. Bubba73 ^{You talkin' to me?} 06:22, 5 December 2012 (UTC)

I don't think any of those are absolute limits of cell phone technology:

1) A cell phone network can be made more reliable than land lines, since, if one tower goes down, it can glom on to the next. If the telephone wire leading to your house is cut, though, that's it, no hope of using it until a repairman is sent out. I just had my land-line go down, but, other than reception problems, have never had a cell phone go dead on me.

2) I actually have better sound quality on my cell phone than land line.

3) Flip phones can be made to answer when you flip them open and hang up when you close them. Clam-shell phones could do the same.

4) Reception can be excellent, if they have enough cell towers.

5) A cell phone with GPS could direct emergency personnel to your location, even if you are cowering up a tree with a grizzly bear below.

There may be one absolute limit of cell phones, though, and that's on comfort. They really can't provide a full-sized headset and still have it be as portable as they want. A compromise might be to place your cell phone in a docking station when home, which could charge it and also tie in to the house phones, and add a bigger antenna, to boot, and maybe a full-sized QWERTY keyboard for texting. StuRat (talk) 06:38, 5 December 2012 (UTC)

Landlines won't go away - they'll just change into something better. The trouble with cellphones and any other sort of radio technology is that it won't scale well. The more users use it for data (internet, video on demand, etc), the more the number of cellphone base stations (towers) and/or the radio bandwith required becomes impossible. More of the current problems with landlines (call quality, reliability, bandwidth) is due to the fact that the Customer Access Network (CAN) ie the copper cable network that connects dwellings and offices to the phone company exchange is old. A lot of cabling is 30 to 50 years old and is just about stuffed - in Australia at any rate. Image the car you might have bought 50 years ago - it would have been reliable back then. But now its rusty and worn out. But they have started rolling out Fibre-To-The-Home (FTTH) to replace the CAN. Because it's new it should be reliable - like a new car. And the communication is via VOIP digital instead of voice frequency analog, so upgrades to what your fixed phone can do will be a lot easier. Ratbone 120.145.196.13 (talk) 06:58, 5 December 2012 (UTC)

I'd argue that land-lines don't scale well, since, if you need to dramatically increase the capacity, at some point you need to lay more wire (or fiber) to every house. That's a lot more work than upgrading the equipment at the cell-towers. StuRat (talk) 16:56, 5 December 2012 (UTC)

I'd avoid bundling like the plague. If your landline is part of the cable service, you have to use the mobile to call for repairs. One less level of redundancy.

Mobile services are generally not very reliable. I've had 4 outages during November, that is one per week (although that's above average) and there was no reception from any secondary tower. Too loose a spacing, I guess. I've never had my landline fail, only my phone.

Mobiles are more prone to failure, too: made in China, and their batteries can fail.

Even if there is a secondary tower, I doubt that the landline would fail more easily than both towers at the same time. I doubt that "more towers" can be extended on demand. The aether can only take so much. That's no problem with landlines; signals will not carry over from a line to the other.

Mobile is susceptible to flooding. A single jammer used by terrorists could take a large chunk out of a mobile service. It's not that easy to kill landlines.

Flooding 2.0 - If too many users are on, the service degrades. At least twice a year (xmas, new year), mobile would go down on me.

Poor sound quality on a landline seems to be an issue related to the phones themselves, not the lines, or the line is already damaged and needs replacement.

"the companies offering landlines have concluded that their extinction is inevitable": Except T-mobile. They extincted their mobile service for half a day.

Phones with GPS, that is actually useful. OTOH, the towers could easily add similarly useful info which would be spoof-proof (tower ID + direction + approximate distance).

Texting vs. faxes: At least faxes have the advantage that you can "print" documents to faxes. No need to type them using a keypad which is no better then your average remote. If you have the time to text, you could as well call and save some time. Even Apple are expected to support phone calls by 2030. - ¡Ouch! (^{hurt me} / _{more pain}) 09:51, 5 December 2012 (UTC)

RE: "the companies offering landlines have concluded that their extinction is inevitable", you seem to have misinterpreted my comment to refer to outages. I mean that they think land-lines will no longer exist at some point. In the US, at least, there's the additional issue that all the taxes go on the land-lines, so you get a minimum of like $30 a month, even if you don't use it. My cell phone, on the other hand, is $7 a month.

As for cell phone networks being overwhelmed by traffic, this has happened on land-lines, too, during holidays. It seems to be less of a problem, lately, though, presumably because cell phones have taken much of this burden off the land-line network. So, this is not an inherent problem with cell phones only.

The advantage of texting, just like an e-mail, is that it doesn't require an immediate response. So, if you're in a meeting, and your significant other wants to ask when you will be home, would you rather have your phone ring, or have a text come in, which you can answer after the meeting ?

The advantage of a full-sized QWERTY keyboard, as in a PC, is that I can touch type, dramatically increasing my speed. Those on a cell phone are just too small to permit this. StuRat (talk) 16:38, 5 December 2012 (UTC)

Where I live I have never experienced a mobile network outage, not even when everything else has gone down. I suspect it's more down to how competitive service providers are in your area. --83.84.137.22 (talk) 16:22, 5 December 2012 (UTC)

Another problem with cell phones is there is a long delay whereas a landline is essentially instantaneous. I often hear myself being echoed back. And on a landline you can talk and listen at the same time, just as in a normal face-to-face conversation. Cell phones don't allow that. Those two things together make talking on a cell phone like the awkward remote TV interviews where there is a delay before the other person starts responding so the interviewer starts talking and at that time the remarks of the first person come back, etc, etc. Bubba73 ^{You talkin' to me?} 16:32, 5 December 2012 (UTC)

I wonder if the 2-way versus 1-way at a time issue is an inherent limitation of cell phones or just a poor implementation. It might be necessary to turn off the speaker when you're talking, to limit echoes, since the speaker and microphone are too close together. I wish they had tri-fold phones which could still be small yet expand out enough so the microphone is actually by your mouth and the speaker is actually by your ear. The increased distance, and sound damping from your head, should make it possible to enable simultaneous 2-way communication without echoes. StuRat (talk) 16:43, 5 December 2012 (UTC)

There are 2 reasons why cell phones do not have two-way simultaneous talking ("duplex working" is the technical term). Firstly, two simultaneous directions requires two radio channels, doubling the bandwidth. Bandwidth is precious and MUST be conserved. Secondly, the transmit power power is up to 1 x 10¹¹ times the recieve level, even though it is only around 200 mW. The tranmist energy overloads the sensitive recieve circuits, even if not on the exact same radio channel. It is readily possibly to fix this problem with what is known as discrete directional filtering, but such filters take up a lot of space, and would take the size and weight of a cellphone back to that of a housebrick, or aborb a lot of power, or both. There is a third, minor, reason: The same computer-like chips in the phone are used to process both transmit and recieve signals. To work in both directions simultaneously, you'd need increased processing grunt, increasing the battery drain. Battery capacity is precious too. Feedback from speaker to microphone is not a problem. The success of the better types of loudspeaking conference phones demostrates the success of the electronic enginner's bag of tricks (hybrids and VOGC's) in that regard. Keit 120.145.164.75 (talk) 01:21, 6 December 2012 (UTC)

Re: "cell phone network can be made more reliable than land lines" back there - I've had a land line for 40 years. I think there have been three times when the service was out. Possibly four times, but I don't think so. So about one outage per 10 years. How many times do I get "no service" on my cell phone? Many. How many times to I call a number and NOTHING happens? Many. How many times are there dropouts on a cell phone? Many. Bubba73 ^{You talkin' to me?} 19:31, 5 December 2012 (UTC)

You're somewhat comparing apples and oranges there if you compare your land-line, used in one location, with a cell phone, used at multiple locations. If you just compare your cell phone, used at home, with your land-line, that's more fair. And, again, just because some cell phone service is crap doesn't mean it always must be, due to limits of the technology. A similar argument could be made on cars, early on: "Those darn horseless carriages break down once a week, but my horse has been reliable for 20 years, so cars will never replace horses". StuRat (talk) 19:38, 5 December 2012 (UTC)

I don't use my cell phone at home because (1) I want to be able to talk indoors, (2) cell phone is too unreliable, (3) sound quality is bad, (4) it is too hard to use. Bubba73 ^{You talkin' to me?} 21:06, 5 December 2012 (UTC)

And another thing - with a landline, you get in the phone book! Very important. Bubba73 ^{You talkin' to me?} 22:22, 5 December 2012 (UTC)

About landlines not overwhelmed any more: If broadband is possible via landline, they can transmit 1000's of connections via the same line. And if they can serve 10% of the broadband users at the same time, they can handle 5 times as many telephone calls, too. No need to share the burden with mobile networks.

"The advantage of texting, just like an e-mail, is that it doesn't require an immediate response": often cited but answering machines exist for a reason. On top of that, there is e-mail, which is actually standardized, unlike SMS. Characters like € or ñ get mangled, not to mention ¡, even if you can produce them on a phone.

About outage frequency and redundancy being "down to how competitive service providers are in your area" - bloody hell, I can be 20,000ft ASL in the himalaya and "click here to find single women in my area"! If they can pull that feat, they can as well maintain the damn network...J/K

I doubt that a cell phone is not full duplex. You cannot flood a phone by a simple countinuous signal like a beep.

I think the pause between transmitting and receiving is caused by the packeting. Cell phones cannot simply transmit the sound samples uncompressed; they have to compress a packet of 1024 samples or so into a 2kbit data packet. (The numbers may be WAY off but the reasoning is the same.) That's an average of only two bits per sample; if they quantized each sample down to 2 bits, the quality would be extremely poor. The downside of packeting is that they must record 1024 samples, encode them, and transmit. Thus the receiving phone can only start playback when the entire packet has been encoded. At 8k samples per second, we have that kind of lag in both directions, and it sums up to at least .256 seconds each. Add to that lag the actual encoding, transmission, and decoding, and it can easily double.

"You're somewhat comparing apples and oranges there if you compare your land-line, used in one location, with a cell phone, used at multiple locations." I don't see that. Apples and samsungs, maybe... and the cell phone is not meant to be used in one place only. If it were, it would have a more reliable connection (I'm not an engineer but I'd suggest copper), it would do away with most electronics, and it would draw its power from a more reliable source than a battery. See where I'm going?

Ahem. The point is that mobile networks don't care about issues with mobile telephones the way they should. Part of that is expected at $7 a month. If there were taxes, many of those issues would probably get resolved. Why not? If there were taxes on mobile calls, there would at least be fewer verbal pollutants walking-and-talking. Result. - ¡Ouch! (^{hurt me} / _{more pain}) 08:33, 6 December 2012 (UTC)

Yesterday I bought two years on my Tracfone for $160, so $6.67 a month, unless you include the $50 phone purchase, then it's $8.75. It's a decent cell phone (Samsung S425G) and service, although I rarely use a phone. If I used it often, I'd need a more expensive plan. The only problem I've had with Tracfone is how incredibly painful it is to transfer a phone number, service days, and minutes from one phone to another. This involved hours on the phone with customer service people who barely speak English, waiting for them to mail me a new SIM card (which required a signature, so they couldn't deliver it with me not home), having to re-enter all the phone numbers into my contact list, etc. You also had to figure out just what chain to follow on their phone machine hell. If you picked the wrong path they would say "Sorry, we are experiencing unusually high call demand, please call back later". If you picked the right path, they would answer immediately.

Of course, having just had an outage on my land-line, it was almost as bad. I didn't have a dial tone, and, since I rarely use the phone and it was before the US elections (meaning, if fixed, it would ring off the hook with politicians, who exempted themselves from the no-call list, bothering me) I decided to just wait and see if they'd fix it on their own. They didn't. A month later I decided to go to their website and request a repair, which involved me going outside to connect to the line out there, to test whether the problem is outside the house or inside. Can you imagine if a 90-year old woman had to do that ? So, customer service is iffy either way. StuRat (talk) 17:57, 6 December 2012 (UTC)

I have Tracfone too, but I don't use it at home. I normally leave it in my car, except when I bring it in to charge. If it rings at home, I don't answer it because I know it is a wrong number, since I don't give out my cellphone number. Bubba73 ^{You talkin' to me?} 17:20, 7 December 2012 (UTC)

I hope you live in Hawaii or someplace else with a year-round moderate climate, since temperature extremes can damage portable electronic devices. Also, even if you don't give your number out, when you call people from it, they get your number by caller ID, and may add it to their list of contacts. StuRat (talk) 00:57, 8 December 2012 (UTC)

And speaking about the reliability of the landline - the last time mine was out, it was because of a broken wire in my house. And the time before that was because of water in my outside box after heavy rains. Bubba73 ^{You talkin' to me?} 17:32, 7 December 2012 (UTC)

Well, those are two examples of failure modes not possible on a cell phone. StuRat (talk) 00:59, 8 December 2012 (UTC)

And that is it. About one failure per decade. I can't count the number of times I had no signal, there were dropouts, or I called and nothing happened on the cell phone. And I don't use it that often. Bubba73 ^{You talkin' to me?} 02:52, 8 December 2012 (UTC)

Wow, I just saw an ad for the home cell phone docking station I advocated above. It's the "Straight Talk wireless home phone". I doubt if it does all the things I suggested, but it's a start. StuRat (talk) 00:52, 8 December 2012 (UTC)

House wall mold sensor?

Is there any substance that can detect mold growth inside walls? such that when mold start to grow it will also grow on a sensor that will alert the house manager? which can then preemptively take action. This is different from measuring the conditions such as temperature an moisture which doesn't indicate actual mold. Electron9 (talk) 13:25, 4 December 2012 (UTC)

In my area, the humidity runs about average and mold grows on moist foods just about anywhere and everywhere you happen to leave it out. I'm fairly sure that the mold spores are widely dispersed from soil and foliage here. Thus, if you taped sterile food or growth medium to a wall or inside it you would quickly grow plenty of mold in a day or two, but that wouldn't indicate anything. I haven't lived in any of the more arid areas of the country though, where the spores might be less of a problem. In addition, the available moisture within the wall will likely differ in different locations. So if you placed dried bread high in the wall, it may remain relatively mold free for a while, until it absorbed enough moisture. But even then, its hygroscopicity will likely differ from the wall materials, such that the moisture conditions differ, especially in areas near window sills, bathrooms and basement walls. Low levels of mold are frequently present anyway, which is why storing clothes in such darkened moist areas is generally not a good idea. Modocc (talk) 14:02, 4 December 2012 (UTC)

That said, the odor of mold/mildew is usually fairly strong and detectable when it does become a problem, thus its likely that an electronic nose will be a very useful maintenance tool. Googling on mold electronic nose appears to bring up some relevant literature. --Modocc (talk) 18:44, 6 December 2012 (UTC)

Neurasthenia

I was reading this article but I don't exactly understand what it is. Is it a psychological disorder or a physical disorder of the nervous system? Thanks. 82.132.210.65 (talk) 14:48, 4 December 2012 (UTC)

Neurasthenia was a 19th century disease concept. It describes a combination of symptoms used by doctors to make the diagnosis. The main symptom was fatigability so severe that the patient felt unable to engage in normal work and normal family and social obligations. The doctors knew that there were no objective structural abnormalities in the body (i.e., no "pathology"). There were many hypotheses of cause. These days patients with those same symptoms are likely to be diagnosed with chronic fatigue syndrome. Both of these conditions are good examples of attempts to provide a social role and medical response for symptoms that are not at all understood at the organ or tissue or cellular level. alteripse (talk) 15:23, 4 December 2012 (UTC)